As many people have mentioned, the F150 is available with relatively high payloads, but the chance of finding that version varies per region and dealership. Oftentimes dealerships that specialize in commercial truck sales also have high payload versions of the 1/2 ton trucks on the lot.
I was recently looking for a new truck and found that most of my local Ford dealerships had trucks with a max payload of about 1250 lbs, but the Chevrolet dealers had crew cab, 4WD trucks with payloads of almost 1900 lbs. In the midwest, the few Ford dealerships I checked did have some trucks on the lot with higher payloads.
You'll probably have to do a regional search and/or special order a specific configuration if you want to get the F150 with HD payload package.
You might also want to ensure that you get tow mirrors with whatever truck you end up buying. They'll cost nearly $1,000 to buy from the parts department...